Flood-depth frequency relations for streams in Alabama

Equations were defined for estimating the depth of water for floods having recurrence intervals of 2, 5, 10, 25, 50, 100, and 200 years on rural and urban streams in Alabama. Multiple regression analyses were made using the ' maximum RSQUARE improvement ' procedures. The dependent variable was the flood depth and the independent variables were 10 basin and climatic characteristics. For rural streams, drainage area size (0.44 to 1,344 sq mi) was the only statistically significant independent variable tested to estimate flood depths in six different hydrologic areas. Other variables affecting flood depth relations are reflected in the equation constant and coefficient for each hydrologic area. These account for differences in geologic and topographic characteristics. For urban streams, drainage area size (0.16 to 83.5 sq mi) and percent impervious area (8.3% to 42.9%) of the basin were the most significant independent variables tested to estimate flood depths. For most streams where the drainage area is > 1,344 sq mi, the drainage basin extends into more than one hydrologic area and the equations presented would not apply. Flood profile data and gaging station records are available from the U.S. Geological Survey for use in estimating flood depths for these large streams. Flood routing and historic flood profiles are also available for many of the large streams which have flood regulation. (Author 's abstract)